1. Technical Field of the Embodiments
The embodiments are generally directed to the field of bio-sensing and the processes for forming bio-sensors.
2. Description of the Related Art
Currently available glucose sensor technology is limited in its efficacy for sensing low glucose concentration in individuals, also called hypoglycemia. Hypoglycemia is a common complication of diabetes and it is very dangerous to people with diabetes especially for new born babies. Hypoglycemia occurs when the glucose concentration in the blood is low and leads to insufficient supply of glucose to the brain. This condition leads to numerous problems ranging from dysphoria to seizures, unconsciousness, and permanent brain damage. The condition may even result in death. Currently, the detection of hypoglycemia is still a challenge for glucose sensors on the market. Current sensors either cannot accurately detect low glucose concentration or there is lag during detection.
The embodiments described herein are directed to a glucose sensor based on carbon nanotube field effect transistor (CNTFET) technology, wherein the process for forming is novel process and includes the controlled deposition of gold (Au) nanoparticles on the carbon nanotubes. Carbon nanotubes and Au nanoparticles possess outstanding electrical and biological properties that make them ideal materials for bio-sensing applications. Through the controlled deposition of Au nanoparticles onto carbon nanotube, the sensitivity of the glucose sensor can be tuned in order to achieve high sensitivity and therefore realizing the detection of hypoglycemia.
Current site-specific Au nanoparticle deposition method involves electrochemical dip-pen nanolithography as described in Chu et al., J. Phys. Chem. 2008, 112, 13437-13441. This method uses atomic force microscopy (AFM) to achieve site specific deposition. As shown in prior art FIG. 1, the tip of the AFM dip-pen is first immersed in a gold chloride solution, and then a voltage is applied to the tip. As the tip sweeps over the carbon nanotube, Au nanoparticles can be deposited onto the carbon nanotube through electrochemical reaction. The result of an exemplary deposition sweep is shown in FIGS. 2a and 2b. The AFM deposition process does not provide for adequate Au location, size or number control to achieve the glucose sensor efficacy required for sensing hypoglycemia.
More particularly, in the AFM deposition process, the locations of the deposition sites are controlled by the location of the AFM tip. Since there is gold chloride solution on the AFM tip, the tip has to be brought to the selected location before starting to sweep across the carbon nanotube, and the location of the tip cannot be controlled precisely. The present embodiments described herein solve this problem by using an electron beam to control the locations of the deposition sites which can easily achieve nanometer scale precision.
Further, in the AFM deposition process, the number of the Au nanoparticles cannot be controlled due to the geometry of the AFM tip. The present embodiments described herein solve this problem since individual Au nanoparticles can be deposited one at a time.
Finally, the AFM deposition process is relatively inefficient. The present embodiments described herein use e-beam lithography to create the deposition sites, which allows for particularity in the deposition patterns. For example, and as described in detailed below, the size of the PMMA opening may be controlled to achieve single Au nanoparticle deposition or multiple Au nanoparticle deposition on a carbon nanotube. Additionally, the present embodiments allow for the creation of multiple PMMA openings at a time, and deposition of Au nanoparticle(s) onto these multiple individual sites at the same time. The AFM deposition process only allows for deposition of the Au nanoparticles onto one site each time since the deposition occurs only when the AFM tip touches the carbon nanotube.
These and other advantages over the prior art sensors and processes are described herein with respect to the present embodiments directed to a novel method to realize in-situ site specific deposition of gold (Au) nanoparticles on single-walled carbon nanotube field effect transistors (CNTFETs) for ultra-sensitive bio-sensing applications, including glucose sensing.